1. Field of the Invention
The present invention relates to a soft mold, and more particularly, to a method for fabricating a soft mold, in which the soft mold is properly used if a size of a master mold is smaller than that of a substrate to be patterned.
2. Discussion of the Related Art
Generally, a soft mold is fabricated by casting a rubber having elasticity in a mold and concaving or embossing a pattern depending on a shape of the mold.
The soft mold is used to form a fine pattern of a micro unit, such as a concave or embossed pattern. For example, the soft mold is used to form either a color filter on a color filter substrate of a liquid crystal display device or an electrode in an organic electroluminescent (EL) device.
The soft mold can be fabricated by curing an elastic polymer. Polydimethylsiloxane (PDMS) is widely used as the elastic polymer. In addition to PDMS, polyurethane or polyimide may be used as the elastic polymer.
Hereinafter, a related art process for fabricating a soft mold will be described with reference to the accompanying drawings.
FIG. 1A to FIG. 1C are sectional views illustrating related art process steps of fabricating a soft mold.
As illustrated in FIG. 1A, a master A is prepared to concave or emboss a predetermined shape on a surface of a soft mold.
The master A is formed in such a manner that an insulating material such as Si3N4 or SiO2 is deposited on an insulating substrate 10 such as a silicon substrate to form a preceding layer and the preceding layer is patterned by a photolithographic process to form a desired pattern 12.
At this time, the pattern 12 on the insulating substrate 10 may be formed of metal, photoresist or wax in addition to Si3N4 or SiO2.
The master A is formed by the aforementioned process steps.
As illustrated in FIG. 1B, if the master A is completed, an elastic polymer (elastic rubber) solution of a pre-polymer state is cast on the master A to form a pre-polymer layer 14. PDMS is used as the elastic polymer.
Subsequently, the pre-polymer layer 14 is cured.
Next, as illustrated in FIG. 1C, a polymer layer in which the pre-polymer layer 14 is completely cured is referred to as a soft mold 16. The soft mold 16 is stripped from the master (‘A’ of FIG. 1B) so that the soft mold concaved or embossed in a predetermined shape on its surface is fabricated.
The related art soft mold is fabricated by the aforementioned process steps.
The soft mold fabricated as above is used in various fields of soft lithography, soft molding, capillary force lithography, and in-plane printing.
For mass production of the product based on the soft mold used in various fields, it is necessary to exactly align the soft mold.
Particularly, in the soft mold for in-plane printing, in case where a master mold is smaller than a substrate to be patterned, a threshold is formed in the mold to cause a problem when a fine pattern is formed.
This case will be described with reference to FIG. 2A and FIG. 2B.
FIG. 2A and FIG. 2B are structural sectional views illustrating a master mold smaller than a substrate to be patterned.
As illustrated in FIG. 2A, after a master mold 22 is arranged on a rectangular mold shaped jig 21, a cured polymer layer 22 is formed in the jig 21 including the master mold 22. A back-plane substrate 24 is attached onto the cured polymer layer 22.
As illustrated in FIG. 2B, in a state that the back-plane substrate 24 is attached to the cured polymer layer 22, the jig 21 and the master mold 22 are stripped from the polymer layer 23 to form a soft mold attached with the back-plane substrate.
Afterwards, a substrate 25 for a fine pattern is arranged below the soft mold.
At this time, the master mold has a size greater than that of the substrate to be patterned.
However, if the substrate 25 to be finely patterned is greater than the master mold as illustrated in FIG. 2B, a threshold is formed at the corner of the mold.
The mold is not closely attached to the substrate 25 due to the threshold. Thus, the mold is spaced apart from the substrate 25 at a certain interval. Particularly, the mold is used for in-plane printing, a problem occurs in that the fine pattern is not formed.